1. Field of the Invention
The present invention relates to fluid distribution and optionally collection in solid waste in landfills; and particularly bioreactive landfills and contaminated sites. In one aspect, the present invention relates to waste treatment liquid collection and recirculation in solid waste in landfills. In another aspect, the present invention relates to remediation of contaminants in the contaminated liquid or contaminated subsurface. In both instances, layer of a permeable, hydraulically conductive material is provided to allow the distribution of the fluids into the layer and from the layer into the landfill or contaminated site. The invention also relates to the use of sensors in the layer to collect data about the surrounding area.
2. Description of Related Art
The key difference between a “dry tomb” landfill and a bioreactor landfill is that bioreactor landfills require controlled addition of leachate or moisture to the solid waste in the landfill. The recirculation of leachate, other liquids, or fluids (e.g., steam, air) to the solid waste in the landfill is a major component in bioreactor landfills. The addition of leachate or moisture increases waste decomposition. Environmental and economical benefits of leachate recirculation for municipal solid waste landfills or bioreactor landfills are well documented. These benefits include a reduction in the leachate treatment and disposal costs, accelerated decomposition and increased settlement of waste resulting in an airspace gain, an increase in the rate of gas production, acceleration in the generation of landfill gas and which results in a potential for higher short-term revenues from a gas-to-energy system, reduction in the risk associated with contamination during off-site transportation, treatment, and disposal of leachate and potential reduction in the post-closure care period and maintenance costs. Risks and drawbacks of leachate recirculation include, a potential decrease in the slope stability of landfills, a potential increase in the leachate head on the liner, if leachate collection system is not designed to efficiently drain injected and recirculated leachate, potential flooding of the gas collection system, and possible leachate seepage from the landfill side slopes, if an adequate buffer distance is not maintained.
The most common leachate recirculation techniques are broadly divided into surface and subsurface applications. Surface applications include direct application of leachate or spray irrigation of leachate on the landfill surface and surface ponding of leachate. Climate dependency, odor problems, interference with daily operations, poor aesthetics, and potential runoff of applied leachate into storm water management system are the drawbacks of surface application techniques. Conventional subsurface application methods include vertical wells and horizontal trenches. Horizontal trenches are most commonly used in relatively new, municipal solid waste landfills. It is most cost effective to install horizontal trenches before the landfill is capped at the design elevation in the landfill cell. Vertical wells can interfere with landfill daily operations. However, vertical wells can be installed after a landfill is capped or can be retrofit into existing landfills. Therefore, vertical wells are most commonly used in retrofit landfills or where implementing horizontal trenches is not feasible or cost effective. Disadvantages and limitations of vertical wells and horizontal trenches include odor problems during installation due to excavation of waste, high capital cost of construction; and non-uniform distribution of leachate due to the formation of “dry zones” or “dry pockets” where injected leachate cannot reach. Such dry zones can reduce the quantity and rate of landfill gas generated. The dry zones can also lead to differential settlement of waste which can result in greater landfill cap maintenance costs. In addition, the amount of leachate that can be recirculated by these methods may not be sufficient to get rid of all leachate typically produced by landfills located in humid regions.
The related patent art for municipal solid waste sites is evidenced by U.S. Pat. Nos. 5,855,664 to Bielecki et al and 6,599,058 to Arnold.
There remains the need for a system and method of distributing and collecting fluids from a portion of a landfill or contaminated site which allows for uniform distribution of the fluid into the landfill or contaminated site and which is economical and easy to install.